The proposed research includes the preparation of additional sequences of human IgC1 and to study their complement fixing properties and their mechanism of action. Further investigations towards securing a small anticomplement fragment of cobra venom factor will also be made. BIBLIOGRAPHIC REFERENCES: "Complement Consuming Compounds: Synthetic Peptides Corresponding to Fragments of the C mu4 and C gamma 2 Domains of IgM and IgG1". B. J. Johnson and K.E. Thames. Fed. Proc. 35:494, 1976. "Studies on the Antigenic Determinants of the Thy-1.2 Alloantigen as Expressed by the Murine Lymphoblastoid Line S-49.1 TB.2.3". B. J. Johnson, U. N. Kucich and A. T. Maurelli, J. Immunol. 116:1669, 1976.